The other night we a couple glasses of wine with dinner and after dinner I decided I wanted a Scotch instead of more wine. My half gallon of Dewars is a little old, 4, 5, years old and the bottle was opened back then. It’s been probably 3 or 4 years since I had any Scotch from that bottle. I generally have a Scotch before dinner when we eat out, though that isn’t often either. So I pour myself a Scotch and water with ice. The first, second and third sips it was sweet like a bourbon. Had to open a new bottle. Has anybody had an experience like this? Can Scotch become sweet over the years after being opened?
No. Dewars is just on the sweet side. Maybe you’ve been drinking nicer whisky recently?
This is the direct effect of oxidation and evaporation.
Depending on the scotch ( usually the chill filtered ones are more subject to this) it will take more or less time but! Once a bottle is opened it oxidise and the reaction can change the flavor profile quite a bit. I discovered this about 10 yeas ago with a Macallan 10yrs, it was simply flat I thought I was drinking a diluted sample. The other phenomenon is evaporation, alchool evaporate without much encouragement. So every thime you open it you ‘change the air’ and restart the evaporation process (as up to a point the aire of the bottle become saturated).
From my experience, when you reach the half of a bottle yu should put a time stamp ( max a year) to empty the bottle. If you have a special one then buy some nitrogen and a special film (used by botanists to fix branches) to seal the cork.
Hope this helps